The goal of this thesis was to enlighten basic principles of the partial oxidation of hydrocarbons and their oxigenates with molecular oxygen under the influence of supercritical water. First the selective oxidation of methanol to formaldehyde without and with heterogeneous silver catalysts was investigated. In the next step the selective oxidation of methane to methanol and propylene to propylene oxide (which reacts further with water to 1,2-propandiole) was examined. Currently this reactions are not satisfactory with respect to conversion and selectivity behaviour. Supercritical water is suitable to stabilize polar intermediates by hydratisation to protect them from further oxidation. Supercritical water as reaction medium offers more potential advantages like the influence on the reaction kinetics via the kinetic pressure effect, a high solubility of coke as well as the low reactivity of water. In addition, water is not toxic, neither combustible nor explosive, well available and neutral to environment. For the investigations a computer controlled high pressure plant was developed. Principal item of this plant is a jet loop reactor. This new reactor type for reactions in supercritical water shows a gradient-free behaviour like an continuous ideal stirred tank reactor. This was confirmed by examining the residence time behaviour and the rate of circulation. The high pressure plant allows parameter variations up to 500 °C and 40 MPa. Feed mass streams are adjustable up to approximately 12 kg h-1 as well as residence times between 0,5 and 60 s. The quantitative analysis took place online by means of infrared spectroscopy, electrochemically and magnetomechanically oxygen analysis as well as offline via gas chromatography, high pressure liquid chromatography, UV-VIS-spektroscopy and atomic absorption spectrometry. Silver was used as a heterogeneous catalyst in form of metal sheets, as granulate and supported. Further more, metal sheets of a gold silver alloy and also splinters of the reactor material, (the nickel basis alloy Inconel 625) were used. It was found that Inconel 625 shows a catalytic effect in the partial oxidation of methanol. The partial oxidation of methanol, methane and propylene in supercritical water with and without heterogeneous catalysts were examined in different test series. Organic feed to oxygen relationship, temperature, pressure and mass stream were varied as well as the residence time. Beside the dependence of selectivity, conversion and yield on the reaction parameters, the reaction order, activation energies and activation volumes could be examined. The partial oxidation of methanol leads to the products formaldehyde, formic acid, CO, CO2, H2 and 1,2-ethanediole. A high formaldehyde selectivity was found only at mild conditions (e. g. at low temperature and short residence time). This also applies for the partial oxidation of methane with respect to the desired product methanol. 1,2-propanediole, acetic aldehyde and CO are the main products of the partial oxidation of propylene. In addition many by-products were formed. In the three reactions examined, the temperature, the organic feed to oxygen ratio and the residence time dominate the selectivity distribution. A selectivity-conversion-problem exists for all three reactions. High selectivities for the desired partial oxidation products are obtained consequently only at low conversion rates of the respective educt. An activation of methanol and propylene by the catalyst and reactor wall surface is possible due to the low activation energies that were determined. Beside the thermal activation of methane in the fluid phase, a metallic activation as in the gas phase reaction is also possible. In all examinations negative activation volumes were obtained. The reaction velocity could be increased by increasing the pressure consequently. The obtained non integer reaction orders indicate complicated reaction mechanisms. During the exposition in supercritical water, corrosion of the reactor wall and the catalyst takes place, that reinforces with low temperatures and high oxygen concentrations. Nevertheless, the reactor material and the metal sheets of silver show a sufficient stability for technical reactions in supercritical water. At certain reaction parameters silver as catalyst favours the selectivity to the desired products. Generally a heterogeneous catalyst shift the selectivity spectrum into the direction of the total oxidation products.